1. Field of the Disclosure
The present invention relates to the technical field of the measurement and evaluation of a characteristic of a heat flux transmitted from a first medium to a second medium or exchanged between a first medium and a second medium. The invention also relates to a method for measuring or evaluating a characteristic of a heat flux transmitted from the first medium to the second medium.
The invention especially relates to systems for measuring and regulating heat flux.
2. Related Art
Measurement of heat flux allows heat loss or gain from an object (for example an oven, a building, etc.) to be quantified. Currently, no sensor allows the variation in amount of heat passing through an object and the variation in its temperature to be predicted in real-time. Such predictive devices would be suitable for systems for the thermal regulation of buildings, for detecting the outbreak of fires, for detecting physical effects (phase changes and material growth, especially crystallization) and also for thermal management of integrated electronic systems.
Thermoelectric converters exist allowing thermal energy to be converted into electrical power by virtue of the “Seebeck” effect, illustrated in FIG. 1. With such a converter, the heat flux φ transferred from a medium the temperature of which is T0 to a medium the temperature of which is T1, can be evaluated. Specifically, by virtue of the Seebeck effect a potential difference V appears across a thermoelectric material A of the converter, the ends of which are subjected to a thermal gradient T1−T0. Operation of such a converter respects the following relationship:V=SA×(T1−T0)=SARthA×φwhereRthA is the thermal resistance of the thermoelectric material A, andSA is the Seebeck coefficient of the thermoelectric material A.
Specifically, the principle of the Seebeck effect is as follows: if a heat flux φ passes through a conductive or semiconductor material causing, on account of the thermal resistance RthA of the material, a temperature gradient ΔT=T1−T0 (where T1>T0) to form between its ends, a potential difference V then forms between the ends of the conductor.
Thermoelectric n-type semiconductors produce an electrical voltage proportional to the negative of the heat flux passing through them and thermoelectric p-type semiconductors produce an electrical voltage proportional to the heat flux passing through them.
Thermoelectric converters and thermoelectric fluxmeters mainly consist of a series of a number (N) of pairs of elements made of thermoelectric materials with different Seebeck coefficients, preferably alternately n-doped (or doped n-type) or p-doped (or doped p-type), the elements being electrically connected in series and thermally connected in parallel, as shown in FIG. 2. These elements are for example placed intermediate between two substrates, for example substrates made of Si, AlN, Al2O3, Al, etc. Moreover, the elements are electrically connected to one another for example by virtue of metal connection elements, such as connection elements made of copper or silver.
During passage of a heat flux φ, the thermoelectric converter or fluxmeter delivers a voltage proportional to this flux:V=N(Sp−Sn)×ΔT=N×Spn×ΔT=N×Spn×φ×Rth where:Spn is the differential Seebeck coefficient between the p-type (p) and n-type (n) elements; andRth is the thermal resistance of the module composed of N thermoelectric p-n pairs thermally connected in parallel.
A fluxmeter therefore allows the amount of heat exchanged between two objects or two media to be quantified. This measurement is proportional to the geometrical or spatial temperature gradient between the ends of the fluxmeter (ΔT=dT/dx=Thot−Tcold), but is not related to the variation of the temperature over time (dT/dt), and therefore does not allow the variation in the temperature of an object through which a heat flux flows to be predicted. The only way that this can be achieved is to develop a sensor or converter that allows a signal proportional to the derivative of the heat flux to be delivered directly.
Generally, devices for measuring flux provide no predictive information on the variation of the temperature of the system, but only on the amount of energy that penetrates into an object. Fluxmeters are sensors or transducers that only allow a spatial temperature difference to be measured.
No known document relating to fluxmeters considers measurement of flux derivatives (or measurement of variation in flux over time) by means of a sensor.
Documents WO 2008/024455, U.S. Pat. No. 5,288,147 and WO 1999/019702 disclose calorimetric systems that employ differential measurements between thermocouples; however these devices only allow a temperature difference between two samples placed in two separate regions to be measured and do not allow the time derivative of the heat flux to be quantified.
U.S. Pat. No. 7,077,563 describes a device allowing a small but abrupt thermal variation linked to the start of growth of a thin film, and based on a differential measurement of two flux in two different positions, to be observed. This device, based on the subtraction of two simultaneous flux measurements allows the variation in heat flux to be observed, but in no way allows the time derivative (variation) of the heat flux to be measured and the variation in the temperature of the system to be predicted.
The aim of the invention is to provide a device for measuring or evaluating a heat flux characteristic allowing the aforementioned problems to be solved and improving known prior-art devices. In particular, the invention provides an evaluating or measuring device allowing a time derivative of a value of the magnitude of a heat flux to be measured or evaluated in real-time.